上一篇https://www.aiwalls.com/kf/201203/124631.html 講到通過NetlinkManager發送uevent 命令到NetlinkHandler 的onEvent，代碼如下：
void NetlinkHandler::onEvent(NetlinkEvent *evt) {
VolumeManager *vm = VolumeManager::Instance();
const char *subsys = evt->getSubsystem();
if (!subsys) {
SLOGW("No subsystem found in netlink event");
return;
}
SLOGD("NetlinkHandler:OnEvent subsys values is %s",subsys);
if (!strcmp(subsys, "block")) {
SLOGD("NetlinkHandler:onEvent");
vm->handleBlockEvent(evt);
}
}
在NetlinkHandler 裡面得一個VolumeManager，當收到的命令為block時調用VolumnManager的handleBlockEvent，如上加紅加粗的代碼。
handleBlockEvent實則是通過一個循環將事先將main事先讀取的配置文件:etc/vold.fstab存進VolumeCollection，得到VolumeCollection的對象，然後調用Volume 的handleBlockEvent，如代碼：
void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
const char *devpath = evt->findParam("DEVPATH");
/* Lookup a volume to handle this device */
VolumeCollection::iterator it;
bool hit = false;
for (it = mVolumes->begin(); it != mVolumes->end(); ++it) {
if (!(*it)->handleBlockEvent(evt)) {
#ifdef NETLINK_DEBUG
SLOGD("Device '%s' event handled by volume %s\n", devpath, (*it)->getLabel());
#endif
hit = true;
break;
}
}
if (!hit) {
#ifdef NETLINK_DEBUG
SLOGW("No volumes handled block event for '%s'", devpath);
#endif
}
看一下Volume 的handleblockEvent代碼：
int Volume::handleBlockEvent(NetlinkEvent *evt) {
errno = ENOSYS;
return -1;
看起來好像沒做什麼事，其實真的實現在於Volume 的子類，DirectVolume，DirectVolme 中重寫瞭handleBlockEvent，看代碼：
int DirectVolume::handleBlockEvent(NetlinkEvent *evt) {
const char *dp = evt->findParam("DEVPATH");
PathCollection::iterator it;
for (it = mPaths->begin(); it != mPaths->end(); ++it) {
if (!strncmp(dp, *it, strlen(*it))) {
/* We can handle this disk */
int action = evt->getAction();
const char *devtype = evt->findParam("DEVTYPE");
if (action == NetlinkEvent::NlActionAdd) {
int major = atoi(evt->findParam("MAJOR"));
int minor = atoi(evt->findParam("MINOR"));
char nodepath[255];
snprintf(nodepath,
sizeof(nodepath), "/dev/block/vold/%d:%d",
major, minor);
if (createDeviceNode(nodepath, major, minor)) {
SLOGE("Error making device node '%s' (%s)", nodepath,
strerror(errno));
}
if (!strcmp(devtype, "disk")) {
handleDiskAdded(dp, evt);
} else {
handlePartitionAdded(dp, evt);
}
} else if (action == NetlinkEvent::NlActionRemove) {
if (!strcmp(devtype, "disk")) {
handleDiskRemoved(dp, evt);
} else {
SLOGD("DirectVolume:handleBlockEvent—>handlePartitionRemoved");
handlePartitionRemoved(dp, evt);
}
} else if (action == NetlinkEvent::NlActionChange) {
if (!strcmp(devtype, "disk")) {
handleDiskChanged(dp, evt);
} else {
handlePartitionChanged(dp, evt);
}
} else {
SLOGW("Ignoring non add/remove/change event");
}
return 0;
}
}
errno = ENODEV;
return -1;
}
因為我的板子還未完善，所以這裡它認為我的sdcard是一個分區，但無關緊要，原理一樣，就根據分區的代碼跟蹤。:handlePartitionRemoved，由於代碼過多，隻貼出核心代碼：
void DirectVolume::handlePartitionRemoved(const char *devpath, NetlinkEvent *evt) {
if ((dev_t) MKDEV(major, minor) == mCurrentlyMountedKdev) {
/*
* Yikes, our mounted partition is going away!
*/
snprintf(msg, sizeof(msg), "Volume %s %s bad removal (%d:%d)",
getLabel(), getMountpoint(), major, minor);
SLOGD("DirectVolume:(dev_t) MKDEV(major, minor) == mCurrentlyMountedKdev:%d,msg is :%s.",mCurrentlyMountedKdev,msg);
mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeBadRemoval,
msg, false);
if (mVm->cleanupAsec(this, true)) {
SLOGE("Failed to cleanup ASEC – unmount will probably fail!");
}
if (Volume::unmountVol(true, false)) {
SLOGE("Failed to unmount volume on bad removal (%s)",
strerror(errno));
// XXX: At this point we're screwed for now
} else {
SLOGD("Crisis averted");
}
}
}
到此，直接調用父類的unmountVol方法，unmountVol會通過setState通知框架狀態改變。代碼太多，隻推薦核心代碼：
int Volume::unmountVol(bool force, bool revert) {
setState(Volume::State_Unmounting);
}
而setState會通過socket將msg消息傳給框架
mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeStateChange,
msg, false);
接下去的步驟是關於socket的操作，就不深入瞭。
小結
到瞭這一步，Vold 向上層反饋的動作基本己經完成，下一篇文章將會講解Framework 如何取得Vold 反饋過來的數據。
摘自 Terry_龍
